Exposure apparatus, method for selecting optical element, and device manufacturing method

ABSTRACT

An exposure apparatus includes a light source configured to generate light having a wavelength of 250 nm or less, an illumination optical system comprising an optical element having synthetic quartz as a lens material and configured to illuminate an original plate using the light generated by the light source, and a projection optical system configured to project a pattern of the original plate onto a substrate. A value of an absorption coefficient of a hydroxyl group of the optical element having an infrared absorption band at 3585 cm −1  is within a range which is determined depending on a wavelength of the light generated by the light source.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an exposure apparatus, amethod for selecting an optical element, and a device manufacturingmethod.

2. Description of the Related Art

In recent years, a light source of a wavelength of 250 nm or less isused in an exposure apparatus. The light source of a wavelength of 250nm or less is, for example, a krypton fluoride (KrF) excimer laser of a248 nm wavelength or argon fluoride (ArF) excimer laser of a 193 nmwavelength.

Generally, light transmissivity of an optical element such as a lensdepends on a wavelength of incident light. For high efficient exposure,a material (lens material) having high light transmissivity is selectedfor an optical element which is used in an optical system of an exposureapparatus. If a laser having a wavelength of 250 nm or less is used asthe light source, synthetic quartz or fluorite is used as the lensmaterial of the optical element. The synthetic quartz has advantagesover fluorite because of its strong mechanical strength, moderate price,and high processability for a diffractive optical element compared tothe fluorite.

Since these laser light sources emit linear polarized light, if thesubstrate is illuminated with unpolarized light, a function to convertpolarized light into unpolarized light is required in an illuminationoptical system of the exposure apparatus. Further, if polarizedillumination is performed, an illumination optical system having afunction to control linear polarized light emitted from a light sourceinto a predetermined polarization state is necessary.

Thus, regardless of whether the light which illuminates the substrate ispolarized light, an optical element of the illumination optical systemwhich is capable of controlling a polarization state is necessary forthe exposure apparatus and synthetic quartz is used as the lens materialof the optical element.

However, there are various synthetic quartz having different properties.Accordingly, not all synthetic quartz is durable as the optical elementused in the illumination optical system of the exposure apparatus. Inother words, properties of some optical elements made of syntheticquartz degrade when exposed to light emitted from the above-describedlight source for a long time.

Under such circumstances, International Publication No. WO 2005/005694discusses a method for determining durability of synthetic quartz as alens material and selecting the synthetic quartz which contains lessimpurities. A degree of impurities is classified, for example, by adensity of undesired matter such as Al or Na or by an absorptioncoefficient value (hereinafter referred to as α value) of an infraredabsorption band at 3585 cm⁻¹ which is dependent on hydroxyl group as animpurity according to JIS C6704.

If an optical element including synthetic quartz having low durabilityis used as a lens material for exposure processing of the substrate fora long time, the optical element blackens and its transmissivity lowersor its birefringence changes, which results in degraded opticalperformance of the exposure apparatus. Thus, International PublicationNo. WO2005/005694 defines only the upper limit of the absorptioncoefficient of an infrared absorption band of a hydroxyl group and usesa lens material that satisfies such requirements regardless of awavelength of the light source.

SUMMARY OF THE INVENTION

The present invention is directed to an exposure apparatus having anoptical element including synthetic quartz as a lens material capable ofreducing degradation of optical performance for a long time and a methodfor selecting the optical element.

According to an aspect of the present invention, an exposure apparatusincludes a light source configured to generate light having a wavelengthof 250 nm or less, an illumination optical system comprising an opticalelement having synthetic quartz as a lens material and configured toilluminate an original plate using the light generated by the lightsource, and a projection optical system configured to project an imageof a pattern of the original plate onto a substrate. A value of anabsorption coefficient of a hydroxyl group of the optical element havingan infrared absorption band at 3585 cm⁻¹ is within a range which isdetermined depending on a wavelength of the light generated by the lightsource.

According to another aspect of the present invention, a method is usedthat selects as an optical system one of a KrF optical system which isirradiated with KrF excimer laser light and an ArF optical system whichis irradiated with ArF excimer laser light, an optical element havingsynthetic quartz as lens material is to be used. If a value of anabsorption coefficient of a hydroxyl group of the optical element havingan infrared absorption band at 3585 cm⁻¹ is within a range of 0.020 cm⁻¹or more but not exceeding 0.100 cm⁻¹, the optical element is selected asavailable for both the KrF optical system and the ArF optical system. Ifa value of the absorption coefficient of the optical element is greaterthan 0.100 cm⁻¹ but not exceeding 0.400 cm⁻¹, the optical element isselected as available for the KrF optical system.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the present invention.

FIG. 1 illustrates a configuration of an exposure apparatus according toan exemplary embodiment of the present invention.

FIG. 2 illustrates a relation between transmissivity and the number oftimes of irradiation when synthetic quartz having different α values iscontinuously irradiated with ArF excimer laser.

FIGS. 3A and 3B illustrate a depolarization unit.

FIG. 4 illustrates a relation between a crystal axis of thedepolarization unit and an optical axis of incident light, apolarization state of the incident light, and a polarization state ofexiting light.

FIG. 5A illustrates an angle of a wedge shape of the depolarizationplate. FIG. 5B illustrates a polarization state of light which passedthrough the depolarization plate in a plane perpendicular to the opticalaxis.

FIG. 6 illustrates a depolarization plate and a half-wavelength platewhich can be switched alternately.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

FIG. 1 illustrates a configuration of an exposure apparatus according toan exemplary embodiment of the present invention.

The exposure apparatus includes illumination optical systems (2 to 13and 121 to 123) configured to illuminate a mask 14 which is an originalplate by a light source 1 having a wavelength of 250 nm or less and aprojection optical system 16 configured to project and expose thepattern of the mask 14 onto a wafer 18 which is a substrate.

The illumination optical system includes an optical element having anabsorption coefficient value of a hydroxyl group having an infraredabsorption band at 3585 cm⁻¹ within a predetermined range which isdetermined depending on a wavelength of the light source 1.

The light source 1 is, for example, a KrF excimer laser of a 248 nmwavelength or an ArF excimer laser of a 193 nm wavelength.

The light generated from the light source 1 is converted into a lightflux having a predetermined shape by a light flux shaping optical system2 and incident on a diffractive optical element 3.

When parallel light is incident on the diffractive optical element 3, apredetermined distribution is formed on a Fourier transform plane of thediffractive optical element. The light emitted from the diffractiveoptical element 3 is Fourier transformed by a Fourier transform lens 4.The diffractive optical element 3 is switchable depending on aneffective light source to be formed. The effective light source refersto an angle distribution of light irradiated onto a surface of the mask14. The effective light source is also equivalent to light intensitydistribution on a pupil plane of the illumination optical system.

The light which is Fourier transformed by the Fourier transform lens 4is converted into a shape such as an annular shape by an illuminationlight modification lens 5. As in the diffractive optical element 3, theillumination light modification lens 5 is switchable depending on theeffective light source to be formed.

A condenser zoom lens 6 passes the light emitted from the illuminationlight modification lens 5 forms an image on an incidence surface of afly-eye lens 7 at a predetermined magnification. The condenser zoom lens6 and the fly-eye lens 7 are substantially in a conjugated relationship.Further, if the condenser zoom lens 6 is a magnification-changeable zoomlens, a light flux area of the incident light on the fly-eye lens 7 canbe adjusted. Then, a plurality of illumination conditions can be set.

The fly-eye lens 7 includes a plurality of micro lenses which arearranged two-dimensionally. A vicinity of an exit surface of the fly-eyelens 7 serves as a pupil plane of the illumination optical system.

The diaphragm member 8 is disposed on the pupil plane to block passageof superfluous light so that a predetermined light distribution can beachieved. A size and a shape of an aperture of the diaphragm member 8can be changed by a diaphragm drive mechanism (not shown).

An illumination lens 9 superimposes light emitted from the effectivelight source which is formed on the vicinity of the exit surface of thefly-eye lens 7 onto a field stop 10. The field stop 10 includes aplurality of movable light-shielding plates which can form a desiredaperture shape so that an exposure area on the irradiation face of themask 14 can be limited. This contributes to limiting an exposure area onthe irradiation surface of the wafer 18 which is a substrate.

Imaging lenses 11 and 13 transfer the aperture shape of the field stop10 onto the mask 14 which is arranged on an illumination target surfacevia a deflecting mirror 12. The mask 14 is held by a mask stage 15 andcontrolled by a control unit (not shown).

The projection optical system 16 is an optical system configured toproject a circuit pattern of the mask 14 onto the wafer 18 with reducedsize. The wafer 18 is set on an image plane of the projection opticalsystem 16. The circuit pattern of the mask 14 is projected andtransferred to the wafer 18 set on the image plane.

A wafer stage 19 holds the wafer 18. The wafer stage 19 is controlled bya control unit (not shown) and moves two-dimensionally in the opticalaxis direction of the projection optical system 16 and also along aplane perpendicular to the optical axis. During exposure, the mask stage15 and the wafer stage 19 are driven in synchronization with each otherin the direction of the arrow in FIG. 1 to perform scanning andexposing.

The exposure apparatus illustrated in FIG. 1 may include adepolarization element or a half-wavelength plate having syntheticquartz as the lens material. The wafer 18 may be illuminated byunpolarized light or polarized light using the depolarization element orthe half-wavelength plate.

According to the present exemplary embodiment, if the wafer 18 is to beexposed with unpolarized light (unpolarized illumination), linearpolarized light emitted from the light source 1 is converted intounpolarized light by an optical element of the light flux shapingoptical system 2. The lens material of the optical element is made ofsynthetic quartz. In this case, for example, a depolarization plate 121and a transparent wedge 122 having synthetic quartz as a lens materialare disposed in the light flux shaping optical system 2 as illustratedin FIGS. 1 and 6.

Further, if the wafer 18 is exposed with polarized light (polarizedillumination), a phase plate 123 having synthetic quartz as a lensmaterial is arranged in the light flux shaping optical system 2 toadjust a oscillating direction of the polarized light. The phase plate123 may be, for example, a half-wavelength plate. To enable switchingbetween polarized illumination and unpolarized illumination, the lightflux shaping optical system 2 may be configured such that thedepolarization plate 121 or the depolarization plate 121 and thetransparent wedge 122 can be replaced with the phase plate 123.

Since the light emitted from the light source 1 is directly incident onthe light flux shaping optical system 2, generally an energy density onthe surface of the optical element of the light flux shaping opticalsystem 2 is high. Accordingly, a lens material as an optical materialhas high durability. Thus, an optical element using synthetic quartz aslens material and irradiated with light from the light source 1 for along time would show little degradation of property (e.g.,transmissivity).

An absorption coefficient value (α value) of a hydroxyl group having aninfrared absorption band at 3585 cm⁻¹ according to the synthetic quartzused in the phase plate 123 is set as follows. If the light source 1 isa KrF excimer laser, synthetic quartz having the α value of 0.020 cm⁻¹or more but not exceeding 0.400 cm⁻¹ is used.

On the other hand, if the light source 1 is an ArF excimer laser,synthetic quartz having the α value of 0.020 cm⁻¹ or more but notexceeding 0.100 cm⁻¹ is used. By using synthetic quartz which isselected according to a wavelength of the light source 1, highdurability against laser can be achieved. Here, α value can be obtainedfrom the intensity of incident light and intensity of transmitted lightwhen light is incident on the lens material.

The above-described absorption coefficient (α value) will be describedin detail. The impurities in synthetic quartz are, for example, hydroxylgroup, Al, Na, and Li. The hydroxyl group makes up for a defect centerin relation with impurities that substitutes for Si or exists as a H2Omolecule included in the crystal.

Since the hydroxyl group includes a certain number of absorption bandsnear 3000 cm⁻¹, there is a close relation between an amount of lightabsorbed by the hydroxyl group and quality of synthetic quartz. If theamount of absorbed light due to the hydroxyl group is large, then manyhydroxyl groups are included in the synthetic quartz as the impurities.If the amount of absorbed light due to the hydroxyl group is small, thena number of hydroxyl groups as the impurities included in the syntheticquartz is small. Thus, it may be assumed that if the α value is large,then durability is low whereas if the α value is small, durability ishigh. However, as described below, this is not always the case.

Thus, an experiment was performed to clarify a relationship betweentransmissivity, durability, and grade such as absorption coefficient, ofsynthetic quartz and light source. This experiment focused on theabsorption coefficient (α value) of a hydroxyl group in synthetic quartzhaving an infrared absorption band at 3585 cm⁻¹ as an index to determinea quality of the synthetic quartz.

In this experiment, several types of synthetic quartz having different αvalues were continuously irradiated with ArF excimer laser or KrFexcimer laser. The experiment was performed for a plurality of times. Apart of the experimental results is illustrated in FIG. 2.

FIG. 2 illustrates a relation between a number of times of irradiation(pulse number) and transmissivity of synthetic quartz A having an αvalue of 0.09 cm⁻¹, synthetic quartz B having an α value of 0.04 cm⁻¹,and synthetic quartz C having an α value of 0.015 cm⁻¹ when thesynthetic quartz is irradiated with ArF excimer laser. Althoughtransmissivity of the synthetic quartz A was reduced 2% soon after theirradiation was started, reduction in transmissivity was moderate afterthen and a sharp reduction in transmissivity was not observed even after200×10⁶ times of irradiation. The transmissivity of the synthetic quartzB showed a small drop of 0.7% soon after the irradiation was started anda sharp reduction in transmissivity was not observed even when its wasirradiated for a long time.

Although transmissivity of the synthetic quartz C having a smaller αvalue than the synthetic quartz A and B showed a small drop soon afterthe irradiation was started, after about 100×10⁶ times of irradiation,the transmissivity showed a sharp reduction. The 200×10⁶ times ofirradiation according to this experiment would correspond to severalyears of typical usage of an actual exposure apparatus.

Thus, as seen from the result of the experiment, when ArF excimer laseris used as the light source of the exposure apparatus, the syntheticquartz A and B are appropriate for use as a lens material of the opticalelement of the exposure apparatus (i.e. an illumination optical systemor a projection optical system), however, the synthetic quartz C is notappropriate.

Further, by repeating similar experiment described above on syntheticquartz having α values different from the α values of the syntheticquartz A through C, it was understood that if the synthetic quartz hasan α value within a range of 0.020 cm⁻¹ or more but not exceeding 0.100cm⁻¹, then the synthetic quartz is appropriate for the use in ArFexcimer laser. Further, by repeating similar experiments described aboveusing KrF excimer laser as the light source, it was found that if the αvalue of the synthetic quartz is within a range of 0.020 cm⁻¹ or morebut not exceeding 0.400 cm⁻¹, the synthetic quartz is appropriate forKrF excimer laser.

As the light source, KrF excimer laser can have wider allowable range ofthe α value than ArF excimer laser. Thus, it is understood that theallowable range of the α value depends on the wavelength of the lightsource. In other words, degree of degradation of transmissivity anddurability of synthetic quartz when exposure is performed for a longtime depends on a wavelength of the light source.

Further, if a value of an infrared absorption coefficient of a hydroxylgroup having the infrared absorption band at 3585 cm⁻¹ is within apredetermined range with upper and lower limits as described above,transmissivity does not drop sharply and high durability is maintained.

However, if the value of the absorption coefficient is smaller than apredetermined value like the synthetic quartz C, transmissivity isgreatly reduced when it is used for a long time and durability becomeslow. Thus, high durability is not always achieved even when the α valueis small.

Accordingly, when exposure is carried out with a light source usingshorter wavelength such as 250 nm or less, by arranging the α value ofthe synthetic quartz within a predetermined range having the lower limitabove zero as described above, high transmissivity of an optical elementusing synthetic quartz can be maintained for a long time.

In this way, synthetic quartz which is appropriate for use in anexposure apparatus can be selected depending on a type of the lightsource and the selected synthetic quartz can be used as the lensmaterial of the optical element of the illumination optical system. Forexample, an optical element using synthetic quartz as lens material canbe selected depending on the two optical systems, namely a KrF opticalsystem which is irradiated with KrF excimer laser or an ArF opticalsystem which is irradiated with ArF excimer laser.

If an absorption coefficient value of a hydroxyl group of an opticalelement having infrared absorption band at 3585 cm⁻¹ is 0.020 cm⁻¹ ormore but not exceeding 0.100 cm⁻¹ as described above, the opticalelement is selected as appropriate for both the KrF optical system andthe ArF optical system. If the absorption coefficient value of theoptical element exceeds 0.100 cm⁻¹ but does not exceed 0.400 cm⁻¹, thenthe optical element is selected as appropriate for the KrF opticalsystem.

Since synthetic quartz has strong birefringence properties, thesynthetic quartz is effectively used in a unit which makes positive useof birefringence. For example, the synthetic quartz is effectively usedin a depolarization unit or an optical integrator. A case where thesynthetic quartz is used as a lens material of the depolarization unitis described below.

In unpolarized illumination, a depolarization unit (depolarizer) such asa unit illustrated in FIG. 3A is used. The depolarization unit includesthe depolarization plate 121 and the transparent wedge 122. A crosssection of the depolarization plate 121 including the optical axis iswedge-shaped. The transparent wedge 122 is arranged so that it has awedge shape inverse to the depolarization plate 121.

The transparent wedge 122 is an auxiliary element configured to correcta direction of the polarized exit light from the depolarization plate121 in a same direction as the incident direction. Wedge angles of thetransparent wedge 122 and the depolarization plate 121 are slightlydifferent according to the difference in the refractive index of theelements. If the exit direction is allowed to be different from theincident direction, then the transparent wedge 122 is not necessarilyused.

FIG. 3B is a cross section of a depolarization unit without thetransparent wedge 122 illustrated in FIG. 3A. The depolarization plate121 uses synthetic quartz as its lens material. As described above, theabsorption coefficient of the synthetic quartz is within a range of theabsorption coefficient which is determined by the wavelength of thelight source 1.

Further, as illustrated in FIG. 4, a crystal axis of the depolarizationplate 121 is arranged so as not to match a main polarization directionof the incident light flux. According to the present exemplaryembodiment, the crystal axis is exemplarily arranged at an angle of 45degrees with respect to the main polarization direction of the lightflux.

FIG. 4 is a perspective view of the depolarization plate 121 in FIG. 3Aillustrating its configuration. As illustrated in FIG. 4, the directionof the crystal axis of the depolarization plate 121 is at an angle of 45degrees with respect to the polarization direction (Y direction) of thelinear polarized light emitted from the light source 1.

The thickness of the depolarization plate 121 is designed so that alight ray (more particularly linear polarized light in the Y direction)that passes the center position of the depolarization plate 121, throughwhich the optical axis passes, is converted into a circularpolarization. However, the light ray that passes the center of thedepolarization plate 121 is not necessarily converted into the circularpolarization. Furthermore, the polarization direction (Y direction) ofthe linear polarized light emitted from the light source and the wedgedirection of the depolarization plate 121 do not need to match with eachother.

A polarization state of the light flux incident on the depolarizationplate 121 is changed continuously or in steps in a certain direction sothat the entire light flux is depolarized to a substantiallynon-polarization state. In order to increase the amount of relativephase change in the exiting light flux, if a diameter of the incidentlight flux is not symmetrical, the wedge direction of the depolarizationplate 121 may be set to match the direction of the maximum diameter.

FIGS. 5A and 5B illustrate a function of the depolarization plate 121illustrated in FIG. 3A. According to the present exemplary embodiment,the polarization state of the light flux which exits the depolarizationplate 121 changes in the vertical direction (Y direction) as illustratedin FIG. 5B.

According to the present exemplary embodiment, the wedge direction(inclination direction) of the depolarization plate 121 matches thepolarization direction of the linear polarized light emitted from thelight source.

Within a range 121A in FIG. 5B, the polarization state continuouslychanges from top to bottom as follows, linear polarized light in Ydirection, counterclockwise ellipse polarization, counterclockwisecircular polarization, counterclockwise ellipse polarization, linearpolarized light in X direction, clockwise ellipse polarization,clockwise circular polarization, clockwise ellipse polarization, andlinear polarized light in Y direction. This change in polarization stateis repeated in the range 121A in the Y direction.

The number of repetitions of the change in polarization state isdetermined depending on a wedge angle θ1 and a thickness of thedepolarization plate 121 illustrated in FIG. 5A and a beam diameter ofthe light emitted from the light source. The wedge angle θ1 and thethickness can be determined depending on a degree of necessarydepolarization. In order to obtain a sufficient depolarization effect,the polarization state may be repeated 5 times or more.

When performing X polarization exposure or Y polarization exposure usingthe exposure apparatus illustrated in FIG. 1, X polarization or Ypolarization is performed by the light flux shaping optical system 2using the above-described phase plate 123.

The phase plate 123 illustrated in FIGS. 1 and 6 includes ahalf-wavelength plate which is made of a single crystal syntheticquartz. The crystal optical axis of the half-wavelength plate isrotatable about the optical axis.

The value of the absorption coefficient of the synthetic quartz used inthe phase plate 123 is within the above-described predetermined range.Further, the phase plate 123 is not limited to a half-wavelength plateand a quarter-wavelength plate may be used.

The light emitted from the light source 1 typically has a degree ofpolarization of 95% or more. Thus, substantially linear polarized lightis incident on the phase plate 123. If the degree of polarization of thelight emitted from the light source 1 is low, an optical element whichexclusively transmits specific polarized light may be arranged upstreamof the phase plate 123.

If the crystal optical axis of the phase plate 123 is set at an angle of0 degree or 90 degrees with respect to the polarization plane of theincident linear polarized light, the linear polarized light incident onthe phase plate 123 passes through the phase plate 123 as it is withoutchanging the polarization plane.

Further, if the crystal optical axis of the phase plate 123 is set at anangle of 45 degrees with respect to the polarization plane of theincident linear polarization light, the linear polarized light incidenton the phase plate 123 is converted into linear polarized light havingthe polarization plane changed by 90 degrees.

If Y-polarized light is incident on the phase plate 123, the phase plate123 is set so that the crystal optical axis of the phase plate 123 is atan angle of 0 degree or 90 degrees with respect to the polarizationplane of the incident Y-polarized light. In this case, the Y-polarizedlight incident on the phase plate 123 passes through the phase plate 123as it is without changing the polarization plane and illuminates themask 14 in the state of the Y-polarized light.

On the other hand, if the crystal optical axis of the phase plate 123 isset at an angle of 45 degrees with respect to the polarization plane ofthe incident light, the polarization plane of the Y-polarized lightincident on the phase plate 123 changes 90 degrees and the Y-polarizedlight is converted into X-polarized light and illuminates the mask 14 inthe state of the X-polarized light.

Synthetic quartz is used as the lens material of the phase plate 123 forperforming the polarization illumination. If the light source 1 is a KrFexcimer laser, synthetic quartz having an α value of 0.020 cm⁻¹ or morebut not exceeding 0.400 cm⁻¹ will be used. If the light source 1 is anArF excimer laser, synthetic quartz having an α value of 0.020 cm⁻¹ ormore but not exceeding 0.100 cm⁻¹ is used.

By using synthetic quartz which is selected according to its α value,high durability can be obtained even if the synthetic quartz is used forpolarized illumination.

Next, a manufacturing method of a device (e.g. a semiconductor ICelement, a liquid crystal display element) using the above-describedexposure apparatus is described. The device is manufactured via anexposure process, a developing process, and other known processes usingthe exposure apparatus according to the above-described exemplaryembodiment. A substrate (such as a wafer or a glass substrate) on whicha photosensitive material is coated is exposed to light in the exposureprocess. The substrate or the photosensitive material is developed inthe developing process. The other known processes are etching, resiststripping, dicing, bonding, and packaging. A high-quality device can bemanufactured according to the device manufacturing method of the presentinvention.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the present inventionis not limited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

This application claims priority from Japanese Patent Application No.2007-182444 filed Jul. 11, 2007, which is hereby incorporated byreference herein in its entirety.

1. An exposure apparatus comprising: a light source configured togenerate light having a wavelength of 250 nm or less; an illuminationoptical system comprising an optical element having synthetic quartz asa lens material and configured to illuminate an original plate using thelight generated by the light source; and a projection optical systemconfigured to project an image of a pattern of the original plate onto asubstrate; wherein a value of an absorption coefficient of a hydroxylgroup of the optical element having an infrared absorption band at 3585cm⁻¹ is within a range which is determined depending on a wavelength ofthe light generated by the light source.
 2. The exposure apparatusaccording to claim 1, wherein the light source is krypton fluorideexcimer laser, and wherein a lower limit of the range is 0.020 cm⁻¹ andan upper limit of the range is 0.400 cm⁻¹.
 3. The exposure apparatusaccording to claim 1, wherein the light source is argon fluoride excimerlaser, and wherein a lower limit of the range is 0.020 cm⁻¹ and an upperlimit of the range is 0.100 cm⁻¹.
 4. The exposure apparatus according toclaim 1, wherein the optical element is a depolarization element.
 5. Theexposure apparatus according to claim 1, wherein the optical element isa phase plate.
 6. The exposure apparatus according to claim 1, wherein avalue of a lower limit of the range is greater than zero.
 7. A methodfor manufacturing a device comprising: exposing a substrate to lightusing the exposure apparatus according to claim 1; and developing theexposed substrate.
 8. A method for selecting as an optical system one ofa krypton fluoride optical system which is irradiated with kryptonfluoride excimer laser light and an argon fluoride optical system whichis irradiated with argon fluoride excimer laser light, the method usingan optical element having synthetic quartz as lens material, the methodcomprising: selecting the optical element as available for both thekrypton fluoride optical system and the argon fluoride optical system ifa value of an absorption coefficient of a hydroxyl group of the opticalelement having an infrared absorption band at 3585 cm⁻¹ is within arange of 0.020 cm⁻¹ or more but not exceeding 0.100 cm⁻¹, and selectingthe optical element as available for the krypton fluoride optical systemif a value of the absorption coefficient of the optical element isgreater than 0.100 cm⁻¹ but not exceeding 0.400 cm⁻¹.